Conventional slate chalkboards used in teaching environments to convey written messages and to display graphic and other visual elements have been a staple in elementary schools and high schools for a very long period of time. For many, chalkboards are also utilized in universities and, in some cases, continue to be a part of people's lives even when they continue to a work environment.
When introduced, chalkboards were generally boards of dark slate that were marked with shards of light slate. Over the years, chalkboards progressed and chalk was used in place of slate shards to write on the board. Further developments in this arena included the use of more durable slate, as well as magnetic chalkboards, which accept magnetic visual aids for teaching purposes. These types of chalkboards are generally made of porcelain on a steel magnetic surface that comes in two easily recognized colors—green and black.
In addition to the foregoing, chalkboards have evolved in other ways by providing for a removable and portable “chalkboard-esqe” surface having properties that allow a user to delineate a chalk mark thereon. For example, U.S. Pat. No. 3,497,969 (“Schwoegler”) teaches a flexible, rollable chalkboard surface. Schwoegler discloses a number of different sheet materials that can be used in connection with the chalkboard surface, including both natural and synthetic materials, such as paper laminates, acetate butyrate, polyvinyl chloride, polyethylene, polypropylene etc. Generally, the chalkboard surface is formed by coating one side of the sheet material with a pigmented coating composition that includes a black or gray pigmented rubber latex paint and a finely divided, mildly abrasive material. Other resinous or plastic materials may be used as well in combination with the mildly abrasive material. A coating of pressure sensitive adhesive is applied to the second side of the sheet material. Releasably attached to the pressure sensitive adhesive coating is a protective sheet which, upon removal, permits the flexible, rollable chalkboard to be mounted on a supporting surface, such as a wall. The chalkboard surface is also removable from the supporting surface after it is attached, and may be stored for later use.
U.S. Pat. No. 4,138,523 (“Katsurayama”) likewise discloses a film material for forming blackboards. The film material comprises polypropylene or polyethylene covered on one surface with a layer of paint, made of polyurethane resin composed of polyol and polyisocyanate. The paint contains a coloring pigment, a bulking agent, such as powdered alumina and powdered calcium carbonate, and in some cases silicon oil or polyethylene wax. Katsurayama discloses that the film is attached to a base board, such as a wooden board, a veneer board, a particle board or fiber board, by means of a conventional plastics adhesive, with the paint layer exposed on the outside.
Although the flexible varieties of prior art chalkboard surfaces appear to have certain advantages, they suffer from at least one major deficiency. In particular, the chalkboard surfaces disclosed by Schwoegler and Katsurayama utilize various types of paint (rubber latex paint in the case of Schwoegler, and polyurethane resin in the case of Katsurayama) in combination with other mildly abrasive materials to form an abrasive layer that enables a user to write on the surface with chalk. Use of a thick and relatively heavy paint in the formation of such flexible chalkboard surfaces adds unwanted weight to the finished product. After being adhesively attached to a supportive surface, the added weight typically causes such flexible chalkboard surfaces to slowly disengage themselves from the supportive surface, even without a user attempting to remove the chalkboard surface from the supportive backing. This is particularly problematic when a chalkboard surface (attached to a wall, door or other form of supportive surface) is vertically oriented, as is customary when writing or displaying messages or other visual indicia.